This invention relates generally to the interaction of a thin film of a liquid stream with a gaseous stream as the liquid passes down contacting surface. More specifically this invention relates to plate structures for vertical falling film contacting or removal of gaseous streams.
Falling film evaporators and reactors are well known in the art and are readily available commercially. Falling film evaporators pass a thin film of a liquid stream down one side of a heat exchange surface in indirect heat exchange with a heating medium that contacts an opposite side of the heat exchange surface and causes an at least partial evaporation of the falling liquid. Falling film reactors comprise a plurality of tubes or plates over which a thin film of one reactant is dispersed for countercurrent or cocurrent contact with a gaseous reactant stream. In the case of evaporation or reaction laminar flow layers in the thin film can inhibit heat transfer and diffusion of vapor.
One of the most well known falling film reactor arrangements is for the continuous sulfonation or sulfation of fluid state organic substances by reaction with sulfur trioxide (sulfuric anhydride) (SO3). In falling film arrangements, the SO3 or other reactant is kept in a gaseous state. The reaction of the SO3 with the organic substances is strongly exothermic throughout the reaction which occurs rapidly or in many cases goes nearly instantaneously to completion. The SO3 is normally diluted with air or other inert gases to a reduced concentration of 4-15 wt-% which attenuates the severity of the reaction. The provision of cooling to the falling film contact surfaces also avoids the generation of temperature peaks from the highly exothermic reaction.
U.S. Pat. No. 3,925,441 issued to Toyoda et al. describes the use of flat plates for falling film sulfonation.
U.S. Pat. No. 5,445,801 to Pisoni describes a tube arrangement for falling film sulfonation that provides improved liquid distribution and accommodates expansion of the tubes.
U.S. Pat. No. 4,059,620 issued to Johnson describes the advantages of maintaining a desired heat exchange profile during the sulfonation of organic compounds with sulfur trioxide.
The sulfonation or reaction of other organic compounds can cause extensive side reactions. Side reactions are best minimized by a uniform distribution of liquid and gaseous reactions over contact surfaces. Systems for controlling the distribution into tubes or plate arrangements for falling film reactors include: weir and dam systems and slit or orifice arrangements that can be mechanically adjusted in various ways. Nevertheless, minor irregularities in the delivery systems to the top of the falling film apparatus can result in substantial flow variations with the attendant drawback of side reaction production. In addition to the problems associated with uniform delivery to a falling film contact surface, variations in the surface also create flow irregularities that can lead to non-uniform contacting and promote side reaction production.
Therefore, a reactor system is sought that will eliminate boundary layer limitations in falling film evaporators or contactors, overcome initial mal-distribution of liquid reactants in a falling film contactor and maintain an equalized distribution of reactants in a uniform film over the contact surface of the reactor.
Accordingly, an object of this invention is to provide an apparatus and process for a falling film contacting surfaces that continually redistributes the liquid film.
Another object of this invention is to provide a falling film reactor arrangement that promotes dispersion of the gaseous reactant through the thin film of liquid.
A yet further object of this invention is to provide a falling film process and arrangement that facilitates indirect heat transfer between the falling film and a heat transfer medium.
These and other objectives are achieved by a falling film device that distributes a liquid stream to a plurality of corrugated contacting columns defined in a vertical arrangement of contacting plates. The corrugations are arranged to have a primary axis that extends at least partially in a direction transverse to the vertical flow of the falling film. Movement of the fluid over the transversely extending corrugations introduces turbulence that disperses the gaseous reactants through the fluid stream for thorough and uniform contacting. Multiple corrugated plates are spaced apart across falling film contacting channels by a distance sufficient to prevent contacting of the falling film with the adjacent plates. A heat transfer fluid may be circulated to contact the sides of the corrugated plates opposite the falling film and thereby provide cooling or heating to the liquid for temperature control. Turbulence introduced by the corrugated plates will again facilitate the indirect heat transfer between the liquid film and the heat transfer medium. In this manner the corrugated plate arrangement provides advantages for the dispersion, contacting and cooling of liquid and gases in a falling film contactor arrangement.
Accordingly, in a broad process embodiment, this invention comprises a process for the contacting of a thin film liquid stream with a gaseous stream. The thin film stream passes down a plurality of corrugated surfaces defined by a plurality of vertically oriented plates. A space sufficient to prevent direct contact between adjacent films separates the adjacent plates over which the thin films descend. A gaseous stream passes through the vertical channels between the adjacent plates for dispersion into or out of the film. The process recovers a process stream from the bottom of the plates.
In another process embodiment, this invention comprises a process for the reaction of a thin film liquid stream with a gaseous reactant. The thin film stream passes down a plurality of corrugated surfaces defined by a plurality of vertically oriented plates. A space sufficient to prevent direct contact between adjacent films separates the adjacent plates over which the thin films descend. A gaseous reactant stream passes upwardly through the vertical channels between the adjacent plates for dispersion into the film. The process recovers a reaction product from the bottom of the plates.
In a more specific process embodiment, the process sulfonates organic substances by passing a stream comprising an organic liquid as a plurality of thin films down corrugated surfaces defined by a plurality of vertically oriented plates. A spacing sufficient to prevent direct contact between the films separates adjacent plates. A gaseous stream containing sulfur trioxide passes through the open vertical channels defined by the vertical plates for dispersion within the thin film. An effluent from the plates comprising a sulfonated reaction product is recovered at the bottom of the channels.
In an apparatus embodiment, this invention comprises a falling film contactor that contains a plurality of corrugated plates positioned in a parallel arrangement to define contacting channels between the adjacent plates. The plates define corrugations that extend at least partially in a horizontal direction. The adjacent plates over which the film passes have sufficient spacing to prevent contacting of liquid films passing over the surface of the adjacent plates. A distribution means provides a uniform distribution of liquid from the tops of the plates over the corrugated surfaces. An additional distribution means receives a gaseous stream through the contacting channels for dispersion into or out of the liquid descending along the plates. Means at the bottom of the plates collect a liquid stream from the contacting channels.
The process and apparatus will ordinarily employ a heat exchange fluid to control the temperature of the reactants in the falling film contactor. The heat transfer fluid passes through channels defined by the opposite side of the contacting plates over which the thin film passes. The degree of heat transfer occurring over the heat transfer surface may be varied by including heat transfer plates between contacting plates. The pitch and number of corrugations on the heat transfer plates may vary over the length of the plates and may vary with respect to the corrugations on the contacting plates to enhance and control heat transfer over the length of the contacting plates.
The arrangement of the corrugations of the contacting plates can be varied to suit the particular characteristics of the process and fluids employed. For low surface tension and low viscosity fluids, a relatively horizontal and shallow pitched corrugation is most beneficially employed. A slight downward pitch may be provided on the horizontal corrugations to provide a transverse movement of liquid and its redistribution as it travels down the reactor. The corrugation sections are preferably in a herring bone pattern so that the fluid flows back and forth in a horizontal direction across the reactor as it moves downwardly over the reactor thereby increasing the redistribution and uniformity of the downward flow. The number and height of corrugation rows can be varied in order to increase the dispersion of liquid reactant descending the corrugations. As the viscosity or surface tension of the liquid reactants in the film increases, the slope of the corrugations and depth of the corrugations may be increased to provide additional redistribution and turbulence. Preferably, any intersection or discontinuity points between corrugations are staggered horizontally to prevent collection and vertical channeling of liquid at corrugation valleys.
Additional details, embodiments, and arrangements of this invention are described in the following xe2x80x9cdetailed description of the invention.xe2x80x9d